(1) Field of the Invention:
This invention relates to friction material such as used in brake blocks, pads and shoes in vehicle braking systems.
(2 ) Description of the Prior Art:
The prior art friction materials have typically included rubber and resin binders, inorganic fillers and asbestos fibers. Glass fibers and glass strands have also been present in the prior art materials as have metal fibers.
The present invention utilizes a processed mineral fiber formed of blast furnace slag such as known in the art as spun slag. The spun slag fibers in combination with the other materials used as disclosed herein result in an unusually efficient brake block material having none of the disadvantages in manufacture or use that have been commonly associated with asbestos fibers in the past.
U.S. Pat. No. 3,365,041 of Jan. 23, 1968 discloses a friction material in the form of a clutch facing which incorporates asbestos fibers and is typical of the prior art.
U.S. Pat. No. 3,390,750 of July 2, 1968 incorporates porous sintered metal fibers in a friction element, for example stainless steel fibers.
U.S. Pat. No. 3,526,306 of Sept. 1, 1970 discloses the use of glass yarn, asbestos fibers, and fine metal wires in a friction element comprising a clutch facing.
U.S. Pat. No. 3,934,686 of Jan. 27, 1976 discloses a friction element in which random textile fibers and/or boron fibers are present.
U.S. Pat. No. 3,956,545 of May 11, 1976 relates to a glass fiber friction element and U.S. Pat. No. 3,959,194 discloses a brake shoe material incorporating cellulosic and/or asbestos fibers.
The present invention differs from the prior art primarily in the utilization of fibers spun from blast furnace slag and the unusual wear and heat resistance qualities of the material resulting from their use.